1. Field of the Invention
The present invention pertains to magnet structures, and more particularly, it pertains to magnet structures for producing a uniform or homogeneous magnetic field within a predefined space such as might be used, for example, in the magnetization/annealing process in the manufacture of thin film magnetic heads.
2. Description of the Prior Art
Dipole magnet structures for producing a strong magnetic field have been used in various industrial or medical applications. For example, in the manufacture of magnetic read/write heads, the soft magnetic material which forms the core of the magnetic head is sputtered or otherwise deposited onto a substrate in a thin film layer and then is typically subjected to an annealing or heat treatment process. During this annealing process, a strong magnetic field is aligned with the axial direction of the thin film head deposition so as to generally align the domains of the soft magnetic material deposition layer so that the individual magnetic heads can produce strong flux fields when they are excited during subsequent read/write operations. Since the magnetic heads are individually quite small and are produced in large quantities (many thousands at a time) on a single deposition layer on a six-inch ceramic or silicon disk, and since a plurality of such disks in a spaced and aligned array are processed at the same time in an annealing oven, it will be apparent that the magnetic field which is utilized during the annealing process must be completely uniform and homogeneous in nature so that each of the individual magnetic heads will be properly aligned therein.
Such magnetic fields are generally produced by a pair of spaced magnetic poles or pole pieces which are arranged perfectly parallel to each other and which are caused to create a magnetic field therebetween either by means of large permanent magnets or by an electromagnetic structure. In order to prevent fringing or expansion about the edges of such magnetic field, which can result in non-uniformity across the field, the peripheral edges of the pole pieces are typically provided by an inclined, forwardly projecting surface. Such pole pieces as used in dipole magnet structures in the medical magnetic resonance imaging industry, for example, can be seen in prior U.S. Pat. No. 4,827,235 to Inomata et al and U.S. Pat. No. 5,754,085 to Danby et al.